Cardiovascular and renal function and their controlling systems have changed during phylogenetic development of the vertebrate in order to adapt to a variety of environments. We intended to define a functional evolution of the kidney, which initially emerged as a primitive excretory device and culminated in the highly specialized mammalian kidney. During the current year, we studied: 1) mechanism of urine formation in the aglomerular toadfish kidney. Urine flow highly depends on divalent ion excretion but not on blood pressure or extracelluar fluid volume. 2) transport properties in isolated rainbow trout tubules. Teh proximal tubules possess electrogenic pump which causes lumen negative potential difference (PD), whereas distal segments showed high lumen positive PD, which was blocked by furosemide. 3) The renin-angiotensin system in the fowl and its role on blood pressure and renal function. More than 50% of vasopressor action by angiotensin appears to be mediated by catecholamine release in the fowl. We have developed antibody against fowl angiotensin I and determined enzymatic properties of plasma and renal renin. Studies on the relationship among blood pressure, renin and catecholamine are in progress. We will continue to determine renal tubular function in primitive animals by using both in vivo and in vitro preparations. The role of the renin-angiotensin system and catecholamines on regulation of cardiovascular and renal homeostasis will be studied in the birds. comparative studies provide unique experimental models which are not obtainable in mammals and provide better understanding into mammalian physiology.